I don't recall how I found out about Julien Green's God's Fool: The Life of Francis of Assisi. Amazon tells me that I ordered it in July of 1998, so perhaps I saw it mentioned on the page for some other book I was thinking of buying.
Back in the late 1990s, I fell in amongst Franciscan companions—none members of any official Franciscan order, but devotees nonetheless. I'd heard of St. Francis, of course, but knew little about him except that he was somehow connected with birds and animals and peace and stuff like that. I went looking for something to read that would tell me more about him.
There are dozens upon dozens, if not hundreds upon hundreds or thousands upon thousands, of books about St. Francis or some aspect of his thought. I read a few of them, but none of them stuck in my mind. I couldn't tell you much about any of them except Chesterton's St. Francis of Assisi, and what I remember most about that is being frustrated that GKC assumed his readers already knew the story of St. Francis. Later I discovered this was his typical method of writing a biography, consisting mostly of what he thought about his subject rather than writing about the subject himself. GKC's thoughts are almost always worth reading, but as an intro to the life of St. Francis, it wasn't working.
I do believe GKC said that every age finds its saint and that St. Francis had been the saint for the Victorian age (though come to think of it, I think he said it in his book about St. Thomas Aquinas); I would suggest that every age finds its St. Francis: the proto-hippy, the pacifist, the revolutionary, the child of nature, you name it. But none of these Saints Francis looked like a man who could change the world.
Julien Green's great accomplishment is to present St. Francis the saint: The man who found Jesus and counted everything else as worthless, throwing his whole life into relentless pursuit of faithful discipleship. There is perhaps a touch of St. Francis the anti-establishmentarian in the book, but it is more than balanced by constant respect for St. Francis the loyal son of the Church, and all is overshadowed by St. Francis the disciple of Jesus Christ.
Here at last was a St. Francis who was a real person. I could see how St. Francis's dream captured hearts and minds across the centuries to the present day. I could see how people met him while he was alive or heard of him years later and said, "I want to be like that!"
I remain not a Franciscan; there are other paths to holiness, and as far as I can tell the one St. Francis followed is not the one for me. But I nevertheless think that St. Francis is one of the greatest saints of the post-Apostolic ages—perhaps even the greatest. And more than any other book, it was God's Fool: The Life of Francis of Assisi that helped me to understand and to see.